I added a Material option to my product but no new variant rows appeared. What did I miss?

An option only creates rows once it has a name and at least one value.

1. Open the product and go to the Variants card.
2. Click + Add another option if you haven't already.
3. Type the name, for example Material, in the Option name box.
4. In Add value + Enter, type a value such as Cotton and press Enter. It appears as a chip. Add the others the same way.
5. The table rebuilds with every combination, for example "M / Red / Cotton".
6. Fill in Price, Qty and SKU for the new rows and click Save.

Be careful: adding a new option changes every combination, so the price, stock and SKU you'd typed on the old rows are cleared. Re-enter them before you save, or click Discard to leave without saving. A product can have up to three options.